Mars Orbiter Camera (MOC) images and Mars Orbiter Laser Altimeter (MOLA) data on the Mars Global Surveyor (MGS) spacecraft show evidence for three catastrophic outflow channels around the Cerberus Plains region, Mars. The morphologies seen in MOC images located within channels seen in gridded MOLA topography are similar to those found in catastrophic flood terrains on Earth, such as the Channeled Scabland. Thus, they indicate the channels' formation by catastrophic flood flow. The morphologies and topography also counterindicate the channels' formation by lava, glaciers or CO₂-charged density flows. Crater counting on lineated terrain, interpreted as diluvially eroded, gives model ages for the channels of extreme Upper Amazonian, ranging from 2-8 Ma for the youngest to 35-140 Ma for the oldest. The distinct age ranges, as well as the geographic/geologic relationships, indicate that the last flood flows down each of the channels were not contemporaneous. Two, and possibly all three, of the channels originate at the Cerberus Fossae volcano-tectonic fissures, although lack of erosion around the channels' origin at the fissures suggests the fissures have been recently reactivated. Neither magmatic melting of ground ice nor gravity-driven groundwater flow can produce a volumetric discharge at a rate commensurate with that estimated from the surface topography. Geomorphic evidence suggests floodwater ponded temporarily in Athabasca Vallis. Two paleoflood height indicators, which are separated by thirty-five kilometers along channel, have very similar heights. This may be explained by temporary ponding of floodwater behind a large crater in the channel, and consequent deposition of sediment in this slower flow. An additional factor contributing to the similar heights of the paleoflood indicators may be post-eruption subsidence near the origin of the channel, although this possibility, without the hypothesized ponding, cannot explain the preferential location of the streamlined forms up slope of the crater.

Chondrules are a major component of primitive meteorites and are thought to be among the first solids to have formed in the solar system. However, the circumstances around the formation of chondrules have remained a mystery for the 200 years that chondrules have been known to exist. In this work, a model is developed to show that shock waves in the nebula could have been responsible for the complex thermal processing that chondrules are thought to have experienced. By studying different sizes of shock waves, it is shown that for shock waves to have been the dominant chondrule producing mechanism in the nebula, the shocks would have to be large (>1000 km) in size. Such shocks may be linked to the formation or evolution of Jupiter within the solar nebula. In addition, the thermal evolution of chondrules by shock waves can explain the geometric properties of compound chondrules if these objects formed by the collisions of molten chondrules. Finally, for the first time, the case of a shock wave passing through an icy region of the solar nebula is studied. It is found that such a situation may have produced conditions that would allow silicates to be hydrated on very short time scales, explaining the presence of phyllosilicates in the accretionary rims around chondrules in CM chondrites.

We use the Tully-Fisher relation (TFR) to compare the behavior of S0 and late-type spiral galaxies. We determine circular velocities based on stellar kinematics derived from stellar absorption line spectroscopy for ten S0s in the Coma Cluster and eight S0s in the Virgo Cluster. We combine these results with similar measurements of thirteen Coma S0 galaxies obtained previously. We find that there is only a small offset, Δm(H) ∼ 0.2, in the H-band luminosity at a given circular velocity, υc ∼ 200 km s⁻¹, between late-type spirals and the S0 data presented here. This result implies a similar total H -band mass-to-light ratio (within an effective radius) among disk galaxies of different Hubble type. As the older stellar population in S0s is dimmer, this suggests a somewhat larger fraction of stellar mass in these S0s than in late-type spirals. These results do not seem to agree with the proposal that star formation in S0s was switched off suddenly a few Gigayears ago due to outside mechanisms and that a large ∼2 mag offset is expected. We also find that the relation between (I- and H-band) luminosity and upsilonc for the S0 galaxies is at best poorly defined and has a scatter of ∼1 mag, significantly larger than the Tully-Fisher relation (TFR) for late-type spirals in clusters, where the observed I- and H-band scatter is σ ∼ 0.3 mag. This substantial scatter is similar to that found in a study of 18 nearby S0 galaxies in the field (Neistein et al. 1999) where σ(I) ∼ 0.7 mag, implying that no tight TFR holds for field S0 galaxies. Our scatter is also much larger than that found by Mathieu et al. (2002) (σ(I) ∼ 0.3 mag) for six nearby S0s. Our results suggest that differing formation histories can lead to S0s with diverse properties and that S0s are more likely to be the outcomes of minor mergers or some "pre-processing" in groups of galaxies falling into clusters, rather than simply late-type spirals that have been stripped of their gas but are kinematically preserved. We suggest that it is likely that many mechanisms, such as slow encounters, tidal interactions, and gas stripping, may have occurred in the lifetimes of the galaxies and produced the heterogeneous class of S0s that we observe today. We also present a study of the dynamics and content of a sample of ten nearby ultraluminous infrared galaxies (ULIRGs) based on 2.3 μm CO absorption line spectroscopy and near-infrared H- and K s-band imaging. Using velocity dispersions derived from the spectroscopy, disk scale-lengths obtained from the imaging, and a set of likely model density profiles, dynamical masses for each ULIRG are calculated and compared to molecular gas mass estimates derived from millimeter interferometric observations and from a standard conversion between ¹²CO emission and H₂ mass. For a majority of the ULIRGs in the sample, we cannot reconcile the large amounts of nuclear molecular gas mass predicted by the standard conversion with our estimates of dynamical masses for the galaxies. Indeed, for several of the galaxies, the calculated molecular gas mass exceeds or completely fills the total dynamical mass budget for the system. Molecular gas masses are found to be up to ten times the dynamical masses. (Abstract shortened by UMI.)

The dynamics of the martian upper atmosphere are not well-understood. I have identified the dominant tidal modes present in the upper atmosphere by comparing density measurements from the aerobraking of the Mars Global Surveyor spacecraft to predictions from classical tidal theory. Other observations and general circulation models have also provided constraints. I have presented a justification for why topography has a strong influence on the tides in the upper atmosphere. I have also studied sol-to-sol variations in density at fixed altitude, latitude, longitude, season, and time of day. I have developed a novel "Balanced Arch" technique to derive pressures and temperature from these density measurements that also estimates the zonal wind speed in the atmosphere. These are the first measurements of winds in the martian upper atmosphere. This technique can also be applied to anticipated data from Titan to measure winds in its upper atmosphere. I have developed techniques to derive density, pressure, and temperature profiles from entry accelerometer data, used them to investigate the entry of Mars Pathfinder, and discovered that surprisingly accurate temperature profiles can be derived without using any aerodynamic information at all. I have also investigated techniques to derive atmospheric properties from the Doppler shift in telemetry from a spacecraft during atmospheric entry and found that a surprisingly robust estimate of temperature at peak acceleration can be derived. I have discovered a network of tectonic ridges in the otherwise bland northern plains of Mars and studied their implications for a possible ocean in that area. I have tested the hypothesis that the formation of lunar crater Giordano Bruno was witnessed in 1178 AD and rejected it due to the lack of any observations of the immense meteor storm that must have followed the crater's formation.

In this thesis, we take the first step toward building a star-formation limited sample of z ∼ 0.8 cluster galaxies with the goal of understanding the physical processes that affect star formation within the cluster environment. We present Hα narrow-band imaging results for four z ∼ 0.8 clusters. We reach 3σ star-formation rate (SFR) limits of ≤ 0.3 h⁻²₁₀₀M(⊙) yr⁻¹, demonstrating that near-infrared, narrow-band imaging centered on the observed wavelength of Hα is a powerful technique for sampling the entire Halpha luminosity function even at relatively high redshifts where Halpha emission moves into the near-infrared. Comparison with optical spectroscopy reveals a significant population of galaxies with Halpha emission but no [OII] emission. The integrated SFR per cluster mass increases with increasing redshift, consistent with the Butcher-Oemler effect. We compare our cluster SFRs with a limited sample of coeval field galaxies and find that cluster galaxies have lower SFRs than their field counterparts. However, a larger sample of coeval field galaxies is needed to make a more conclusive comparison. We model cluster infall using the extended Press-Schecter approach where we assume that the integrated star formation is dominated by galaxies that have been accreted during the last gigayear. The results show reasonable agreement for four out of seven clusters but differ by more than a factor of two for the remaining three clusters. A larger sample of clusters at similar redshifts will provide a more complete census of cluster star-formation properties and will allow a cleaner comparison with our infall model. We will continue to build such a sample of z ∼ 0.8 clusters.

As a whole this dissertation aims to understand giant planets as an entire class of astronomical objects. Initially we investigate the mechanics and evolutionary effects of phase separation in the deep interiors of giant planets. We present the first models of Saturn and Jupiter to couple their evolution to both a radiative-atmosphere grid and to high-pressure phase diagrams of hydrogen with helium and other admixtures. We find that previously calculated hydrogen-helium phase diagrams in which Saturn's interior reaches a region of predicted helium immiscibility do not allow enough energy release to prolong Saturn's cooling to its known age and effective temperature. We explore modifications to published phase diagrams that would lead to greater energy release. Alternatively, we also explore the evolutionary effects of the phase separation of an icy component. We then expand our inhomogeneous evolutionary models to the evolution of hypothetical extrasolar giant planets (EGPs) in the 0.15 to 3.0 Jupiter mass range, incorporating helium phase separation using the hydrogen-helium phase diagram we have calibrated to Jupiter and Saturn. We show how phase separation increases the luminosity, effective temperature, and radii, and decreases the atmospheric helium mass fraction, for various giant planets as a function of age. We also show the effects of irradiation and dense cores. Next we turn to the atmosphere of the transiting EGP, HD209458b. Using a self-consistent atmosphere code, we construct a new model of the planet's atmosphere to investigate the disparity between the observed strength of the sodium absorption feature at 589 nm and the predictions of previous models. For the atmospheric temperature-pressure profile we derive, silicate and iron clouds reside at a pressure of several mbar in the planet's atmosphere. These clouds lead to increased absorption in bands directly adjacent to the sodium line core. Using a non-LTE sodium ionization model, we show that ionization leads to a slight weakening of the sodium feature. The sensitivity of our conclusions to the derived atmospheric temperature-pressure profile is discussed. We show how our investigation leads to a better understanding of how the planetary radius measurements should be compared to model radii.

For my Ph.D. research I investigated the prospects for characterizing transiting extrasolar giant planets from their transit lightcurves. Hubble Space Telescope photometry of transiting planet HD209458b revealed that the planet has no moons. Here, I show that tidal orbital evolution of moons limits their lifetimes, and hence that no moons larger than Amalthea in size should survive around HD209458b, consistent with observations. I then calculate the detectability and scientific potential of planetary rings and oblateness. Oblateness will prove difficult to reliably detect, even with the Hubble Space Telescope. However, large Saturn-like ring systems should be easy to find around transiting extrasolar giant planets if such rings exist.

Infrared detection of water ice phase can reveal the temperature and radiation history of a surface. In this dissertation, I will describe and quantify the process of amorphization of crystalline ice through lab experiments and computer simulations. I will then show how these measurements can be applied to ground based observations. The amorphous phase of solid water forms at temperatures less than 130 K, and converts to crystalline ice at 135 K in an exothermic and irreversible reaction. The amorphous and crystalline phases have distinctive spectra in the infrared. However, ion irradiation of crystalline water ice in the lab makes the infrared spectrum indistinguishable from that of amorphous ice. If the process of amorphization can be quantified, the model can be applied to various planetary surfaces, using an estimate of the temperature and the radiation environment. This work sheds light on the physical processes behind amorphization. I will show that the irradiation of crystalline ice does not create the amorphous phase of ice, but produces a sample that is spectrally indistinguishable from amorphous water ice. The changes in the spectral features are caused by the breaking of OH and hydrogen bonds among other processes. The temperature dependence of this process is a function of the ability of free hydrogen and oxygen to reform the crystalline lattice.

I investigate statistical properties of one-dimensional fields in the universe such as the Lyα forest (Lyα absorptions in the quasar spectrum) and inverted line-of-sight densities. The Lyα forest has opened a great window for studying the large-scale structure of the universe, because it can probe the cosmic density field over a wide range of redshift at relatively high resolution, which has not been easily accessible with other types of observations. The power spectrum completely characterizes Gaussian random fields. However, because of gravitational clustering, the cosmic density field is already quite non-Gaussian on scales below 10 h⁻¹Mpc at redshift z = 3. I analyze the covariance of the one-dimensional mass power spectrum, which involves a fourth-order statistic, the trispectrum. The covariance indicates that Fourier modes in the cosmic density field are highly correlated and that the variance of the measured one-dimensional mass power spectrum is much higher than the expectation for Gaussian random fields. It is found that rare high-density structures contribute significantly to the covariance. The window function due to the length of lines of sight introduces additional correlations between different Fourier modes. In practice, one observes quasar spectra instead of one-dimensional density fields. As such, flux power spectrum has been the basis of many works. I show that the nonlinear transform between density and flux quenches the fluctuations so that the flux power spectrum is less sensitive to cosmological parameters than the one-dimensional mass power spectrum. The covariance of the flux power spectrum is nearly Gaussian, which suggests that higher-order statistics may be less effective for the flux. Finally, I provide a method for inverting Lyα forests and obtaining line-of-sight densities, so that statistics can be measured from one-dimensional density fields directly.

Orbital datasets can be combined and manipulated to learn about the three-dimensional structure of planetary surfaces, and the processes that have acted on them. The Mars Orbital Camera (MOC) is providing high-resolution images. These images allow qualitative inspection of features, and contain quantitative information about the shape of the surface. Using a photoclinometry technique derived from a lunar-Lambert photometric function, I am able to obtain estimates of the down-sun slope of each pixel in an image. This technique was calibrated against synthetic topography, compared to an area photoclinometry technique, and applied to the Viking and Pathfinder landing sites. It is a robust technique for obtaining the roughness and slope characteristics of large areas. It was applied to the potential landing sites for the Mars Exploration Rovers to evaluate site safety. The slopes from this point photoclinometry technique can be used to obtain a rough estimate of topography, which I used in a number of studies where topographic information was crucial. MOC images have shown that layering is pervasive on the martian surface. Mars Orbital Laser Altimeter (MOLA) data can be registered to MOC images to provide elevation constraints on layer outcrops. Such layers are observed in eastern Coprates Chasma both in the chasma rim and in a flat-topped massif. Observations indicate that the chasma stratigraphy consists of thin sequences of resistant layers and intervening thicker sequences of relatively less resistant layers. More resistant units cap the massif against erosion and result in steeper slopes than the weaker units would otherwise allow. These resistant layers can be used as stratigraphic markers which have allowed me to measure the subsidence and tilting of the massif relative to the chasma walls, providing evidence for tectonic motion in this portion of the Valles Marineris. These outcrops indicate that some of these layers may be analogus to terristrial flood basalts in both composition and extent. I have constrained the dip angle of finely layered sequences in Ganges and Hebes Mensae. These layers are either flat lying or dip shallowly, but do not dip steeply, which places some constraints on the origin of these mensae.